The present invention is directed to xe2x80x9cactive implantable medical devicesxe2x80x9d as such devices are defined by the Jun. 20, 1990 directive 90/385/CEE of the Council of the European Communities. This definition includes pacemaker, defibrillator, cardiovertor and/or multisite devices for the treatment of the disorders of the cardiac rhythm, but also includes neurological apparatuses, medical substance diffusion pumps, cochlear implants, implanted biological sensors, etc., as well as the devices for the measurement of pH or an intra-corporal impedance (such as the measurement of the transpulmonary impedance or the intracardiac impedance).
The invention more particularly relates to the functions of processing and recording data over a long period of time, several days to several months and particularly for so-called xe2x80x9cHolter dataxe2x80x9d relating to the cardiac activity of a patient.
The present description refers mainly to the so-called and well known Holter functions that are controlled by implanted devices such as pacemaker, cardiovertor or defibrillator devices, in particular by the implanted device that can be interrogated subsequently by telemetry by use of an external device known as a xe2x80x9cprogrammer.xe2x80x9d
The invention, however, also can be applied to the case of a simple external Holter apparatus, having for its only function the monitoring and the recording of the cardiac activity.
In the same manner, although the description mainly refers to the cardiac signals collected by means of implanted electrodes, the functions performed by the invention also can be applied to other signals collected (sensed) by implanted as well as external electrodes, as well as to event counters or to signals that are not collected but are representative of a state or an action of the implant or of the patient, for example, the application of a shock therapy, the measurement of an impedance of a lead, etc.
The storage of these various data can be carried out in various ways.
A first technique, known as cumulative storage, involves preserving the data in an undifferentiated manner during the whole of the recording period (typically, over a six-month period for patient follow-up). This storage technique includes time-stamping each event using a marker that will be used as a temporal reference mark when the data are processed after being read by the programmer, so as to reconstitute the chronology of the various successive events recorded. This technique is economical in terms of the required memory size, but it is limited to the memorizing (recording) of specific events and does not allow one to monitor (and record) parameters that are continuously varying, for example, to study the evolution of the average heart rate, of an impedance, or of an index of apnea, etc.
Another technique concerns allotting a memory field to each interval of time (typically one day), where the data corresponding to each one of these periods are memorized, in particular for monitoring the evolution of continuously varying parameters. By allotting a memory field for the data collected during the same day, one can thus store such data over an extended period of time, typically up to six months, day by day. After the reading of the data by the programmer, it is possible to carry out a certain number of data-processing treatments, of a statistical nature or otherwise, relatively complete treatments insofar as the data were preserved identically over the whole duration of the six months period. On the other hand, this technique requires large memory resources because of the very great number of memory fields that would be necessary, for example, approximately 6xc3x9730=180 memory fields for a history over six months (assuming 30 days per month) such that each field would store the data collected over 24 hours.
A compromise must therefore be made between the total period of coverage and the precision of the memorized data within each time period: if one wants a precise follow-up, one can, for example, record 2 day periods, but the whole of the recording will cover only one month (14xc3x972 days); if on the other hand one wants to cover a longer time period, for example, six months, it will be necessary to choose less precise time periods, for example, one week.
The invention proposes an apparatus and a process of processing and memorizing data to be recorded over a long period of time, including but not limited to Holter data, making it possible to overcome these various disadvantages, in particular by optimizing the occupation of the memory. Memory size is a particularly constraining parameter in a miniaturized and implanted medical device.
Broadly, the present invention proposes to carry out a differentiated storage of the short-term data and the long-term data. In one embodiment, the short-term data are memorized over a first time period that is relatively short with a relatively high degree of resolution (for example, data are stored in a series of short blocks of time, e.g., one hour, covering one or two days by the time period of one hour), while the long-term data are stored over a second time period that is a relatively long period with a lower degree of resolution (for example, data covering a six month period is stored by one day time periods).
One of the starting points of the present invention is the inventor""s observation that, when Holter data recorded in an implant are analyzed, the precision of the data is important only over the few hours which immediately precede the interrogation, i.e., the reading of the memorized data by the remote programmer, whereas over the weeks or the months which precede those few hours only the general trend of the Holter data and the evolution of such parameter(s) is important to evaluate. For example, if a diagnosis is carried out following a defibrillation shock applied by the apparatus, it will be essential to have a detailed summary of the events which have occurred during a defined period immediately preceding the shock, e.g., 24 or 48 hours or more, in particular including the chronology of the events. For the period prior to the defined period, an analysis of the trend of the events will be generally sufficient.
Indeed, it is believed to be more important to have a follow-up for the time preceding the consultation because: (i) if the patient consults a physician or therapist for a symptom or an awkward or undesirable event, it is extremely probable that this event is recent, and (ii) at the time of the interrogation of the patient, the present invention permits memorizing and reading data reflecting more precise indications over the defined time period (typically one or two days which preceded the consultation and interrogation as compared to data that was recorded 3 or 4 months ago. In other words, the precision of the recording follows the precision of the memory of the patient.
This differentiated storage data recorded over time implies a periodic update of the memory. In one example, during the defined time period, the data is recorded on an hour by hour basis. At the end of the defined time period, each of the hourly recordings are consolidated into data representative of the defined time period. Then, a number of such consolidated data corresponding to successive defined time periods are stored in memory to cover a long term time period. Similarly, new data are recorded hourly as the next defined time period elapses. As the long term period is reached, the oldest consolidated data is replaced by the consolidated data from most recent defined time period. In another embodiment, the data representations are stored by short time periods of one hour over a defined period of one day, and then every day these data of the short time periods are consolidated, i.e., condensed into a consolidated data representing the defined one day period of time. Then, a number of the consolidated data are retained over a longer time period of a corresponding number of days (which may be days, weeks or months). In this manner, one obtains two recordings having sliding and overlapping time windows (one in the short-term and the other in the long-term), which makes it possible to have a condensed long-term follow-up providing the general trends, and a short-term follow-up that is more precise on the most recently occurring events. The size of the memory to be used will be important in selecting the length of the short term, defined, and long term periods.
One preferred embodiment of the invention proposes a process for storing data in a differentiated manner characterized by the steps of:
a) memorizing in a first memory sector a detailed representation of the data over a first plurality of first time periods the first plurality of first time periods following one another over a second time period, preferably the first time periods are successive one hour intervals and each second time period is the defined time period and is one day;
b) periodically, reading in the first memory sector the detailed data representation and processing said detailed data representation to produce, over a third time period, a consolidated representation of the data memorized over said first plurality of first periods, preferably the third time period is a daily interval corresponding to the second period;
c) cumulatively memorizing in a second memory sector the consolidated representations, to give a representation of the data over a plurality of third time periods following one another over a fourth period, preferably, the fourth time period is a period of several days or several months, and the third time periods are successive; and
d) freeing a portion of the first memory sector to allow to memorize therein a detailed representation of new data for another second period.
It should be understood that the second and third time periods may be the same interval, e.g., one day.
In a preferred embodiment, steps b) with d) can be carried out at the end of each second time period, such that the consolidated representation stored at step b) is elaborated starting from the data of the penultimate second time period, so that the detailed representation over the most recent second time period remains stored.
The detailed representation of the data can in particular include:
elaborating a histogram of values over the successive first intervals, i.e., short intervals, with the processing at step b) including the addition of the values to form a consolidated histogram;
values of a parameter measured during each successive first time period, ie., the short time period, with the processing at step b) including the calculation of an average value of the measured values, or alternately the selection of the minimum value and/or maximum value reached by the measured values during the second time period;
an indicator of the occurrence of an event, or presence of a state of operation of the device or of the patient, during each successive first time period, i.e., the short interval, with the processing at step b) including the positioning of a marker in the event of the presence of at least one of the aforesaid indicators during the second time period, or the determination of a number of occurrences of the aforesaid indicator during said second time period.